And what would you suggest? If it's 1/4 tile board that's not water proof and may act like a sponge since you could not lay down a vaper barrier and thin set it in place.
I've done a few dozen of them in my area including my own slab home that the slab sets below grade (and it's got a really high water table) by sealing the floor, adding a 6 Mil. vaper barrier, use 1-1/2 Tap-Cons (The slabs going to be 4" thick) and a dab of silicone shot into the holes before the screw goes in and have never had a call back.
Last edited by joecaption; 11-18-2011 at 04:16 PM.